1. Field of the Invention
This invention relates to a method for separating contaminated resins from particulate materials such as soils, which resins are contaminated with a variety of contaminants, such as heavy metals, radioactive compounds and organics, often in combination, through fluidization of the soil/resin mixture, removal of soil particles not fluidized, and separation of the fluidized resins from those soil particles which are fluidized.
2. Background Information
Contaminated soil and groundwater is becoming a more serious environmental problem every day. The contaminants can include heavy metals, such as for instance, copper, lead and mercury; radioactive species, such as for example, radium, uranium and thorium; and organics, such as for example, oils, grease, polychlorinated biphenyls, (PCB's), benzylamine hydrochloride, flue soot and others.
Various techniques have been developed to remove specific contaminants from soil and groundwater. For instance, heavy metals are known to be found predominantly in the silt, humic or clay fraction of soil. Hence, they can sometimes be removed by size separation techniques, such as tiltable tables, concurrent flow in a mineral jig and by chemical techniques, such as the use of leachates. The radioactive compounds, when originating as a spill, can sometimes be removed to a large extent by leaching. Since these compounds are often also present in the finer particles, the most severely contaminated fraction can also be removed by countercurrent flow size separation. Organics can sometimes be removed by washing with surfactants, thermal treatment or biological processes.
Special problems develop when the different types of contaminants are present in the same soil and/or groundwater. Generally, biological or thermal processes are more effective for removing organics than washing, in the case of finer grain soils and clays. However, toxic inorganics such as lead or chromium (+6), if present, tend to deactivate biological systems due to their toxicity and aggravate air pollution problems endemic to thermal destruction processes. In addition, thermal processes may mobilize contaminants that were otherwise fixed in the treated soil.
Radioactive contamination (e.g., uranium, thorium radium, etc.) can sometimes be removed by soil washing, which can provide a means to process soils having multiple contaminants. The washed soil is compatible with subsequent biological or thermal treatment. Inorganic and radioactive compounds may be separated from organics for sale or disposal.
Many soil washing processes are presently available. Most of these processes use mine equipment to provide intimate soil/extractant contact. U.S. Pat. No. 4,783,253 discloses a process for separating radioactive contaminants from soil using a concurrent flow of water to float away lighter uncontaminated particles from heavy contaminated particles. The slurry of lighter particles is dewatered using a spiral classifier, centrifuge, filter or the like. U.S. Pat. No. 4,783,263 is directed to a process for removing toxic or hazardous substances, in particular organics, from soils and the like by converting the material to a slurry, adding surfactants and/or alkaline agents, and concentrating the toxic substance in the liquid phase, preferably with a modifier in a froth flotation cell.
In certain cases, contamination has been found to be concentrated in ion exchange materials that have accidentally been spilled onto the soil. This is likely to be a problem at any mining site or processing facility which utilizes resins in its processes. Also, the addition of resins to contaminated soils has been found to be an effective means for concentrating the contaminants, and thus decontaminating the soil. Because of the high affinity of the ion exchange resins for the contaminants, however, the contaminants cannot be readily extracted or mobilized from the resins. The contaminated resins must therefore be segregated from the soil.
There is thus a need for an improved process for treating particulate materials, such as soil and the like, contaminated with a mixture of wastes such as radioactive materials, organics and heavy metals.
There is yet another need for such a process which is not capital intensive, is economical to operate and can be made portable for on-site treatment.
There is a further need for a system that can effectively recover the contaminants once they have been removed from the soil, requiring a minimal amount of equipment, chemicals, and being portable to the job site, which further allows for the processing of recovered contaminants, such as metals, through mining and/or smelting operations.
There is yet an additional need for such a process which may be used to treat soils which contain contaminated resins, such as ion exchange materials.
As used herein, the term "fluid" is intended to include both compressible and incompressible fluids, such as liquids, gasses, mixtures and solutions thereof.
As used herein, the term "soil" includes all forms of particulate matter to which contaminants may adhere, such as, for example, clay, fines, sand, rock, humus, etc.
As used herein, the term "heavy metal contaminants" includes both radioactive and non-radioactive metals, and is otherwise intended to encompass the full breadth of metal contaminants known to those skilled in the art.
As used herein, the term "organic contaminants" is intended to refer to all organic compounds which tend to adhere to soil, and which present environmental hazards when permitted to remain in the soil or groundwater.